Glossary of Terms

Default field

A field with no name of its own, directly within a tag. The behaviour of the default field depends on the tag. For example, the default field of a <button> tag contains the text or other content to be displayed inside the button.

Document

The visual user interface of an app, as rendered on the screen for the user to interact with. The 'document' is the live-rendered result of the ioL code and content output by an app.

Document tree

Field

A

Tag

A call to create an object, invoke an action and/or or yield a value.
Tags are generally enclosed in angle brackets < > to differentiate them from regular output. The angle brackets may also enclose field initialisers, default field values, and an object name if present. In some cases where there is no ambiguity, the angle brackets are not required.

Value

A piece of data. A value may be a single number, a string of text (zero or more characters), a reference to an object, or one of the following special values: null, true, false, inf, invalid.

Yield value

A tag yields a result when it returns one or more values back into the document tree.
A tag, when invoked, may yield zero or more values, depending on the tag and how it is being used. Some tags never yield a result value, while some others always yield a single scalar value, and others still may yield a list of zero or more values.
When a tag yields a result value, that value is appended to the parent field that contains the tag.
Unlike return values in procedural programming languages, an object in the document tree may yield values at any time before completion.